The Csrss.exe process is an official process that runs on the Microsoft Windows operating system. So if you see this process, it’s probably not a virus.
Some forums have suggested there is also a Csrss.exe Trojan Horse Virus. From all my experience with Windows, that’s not likely to be something you need to worry about. I’ve never seen two processes with the same name where one of them is an official critical process and the other a Trojan Horse. But I have done due diligence and researched this topic just to make sure. According to Greg Newton on SuperUser, you can have two mysqld.exe processes with the same name if they are in separate folders. This isn’t directly related to processes running on Windows but it’s potentially relevant information. It caused me to keep looking. And I did find Mario S on Stack Overflow who just happened to be not only talking about noticing two Windows processes but the processes he was referring to being Csrss.exe.
The conclusion back then was that both processes are likely still official Windows processes and that if you were to kill any of them, the operating system would crash. Another person suggested that Csrss.exe is a critical system process and even if you do see two of them you shouldn’t want to kill them.
That’s the best information I could find. According to some sources, somewhere out there a Csrss.exe Trojan exists. I don’t know if I believe it, but I’m open to the idea. Regardless, even if you do see two Csrss.exe processes, I wouldn’t assume one of them is a Trojan. I would only worry if Task Manager shows me that the Csrss.exe process is using an unusual amount of my overall computer resources. If it isn’t using excessive resources, I would assume it’s a critical Windows process that I should just leave alone.
If it makes you feel any better, you can run an antimalware scan with a tool like Spybot Search and Destroy and see if it removes it.